1. Field of the Invention
The present invention relates to a power source apparatus with a plurality of batteries stacked together, and primarily relates to a battery system used as a power source for a motor that drives a vehicle such as a hybrid car (hybrid vehicle; HV, hybrid electric vehicle; HEV), plug-in hybrid car (plug-in hybrid electric vehicle; PHEV), or electric automobile (electric vehicle; EV).
2. Description of the Related Art
A high-current, high-output voltage battery system used to power a motor that drives a vehicle such as a hybrid car, plug-in hybrid, or electric automobile has a plurality of batteries stacked together and electrically connected to deliver high output. Adjacent battery electrode terminals are connected via bus-bars, and current flows through those bus-bars for electrical connection.
Methods of electrically connecting a plurality of stacked batteries together include series-connection and parallel-connection. Further, those two methods combine as parallel-connected groups of multiple batteries connected in series (multiple series-parallel) and series-connected groups of multiple batteries connected in parallel (multiple parallel-series). When connecting a plurality of batteries, the connection method should be selected according to the performance required from the batteries employed.
If we assume the use of the same number of batteries with the same performance, series-connection results in higher battery voltage than parallel-connection and is primarily suitable for a hybrid car that demands high-power. In contrast, parallel-connection results in higher battery capacity than series-connection and is primarily suitable for an electric automobile that can be driven a long distance with a single battery charge.
Battery capability required for a vehicle such as a plug-in hybrid is between that required for a hybrid car and an electric automobile. Accordingly, series and parallel combinations are used and batteries are connected in multiple series-parallel (parallel-connected groups of multiple batteries connected in series) or multiple parallel-series (series-connected groups of multiple batteries connected in parallel).
Compared with multiple series-parallel connection, multiple parallel-series connection can detect the state of all the batteries with a limited number of battery state detection lines. Further, since voltage variation between parallel-connected batteries is low and since the detection circuitry is not complex, battery and safety-related control can be simplified in a multiple parallel-series connected system. In addition, the number of bus-bars needed to connect individual batteries together is small allowing the number of component parts to be reduced. Consequently, the overall battery structure can be made compact allowing advantageous use in vehicle applications demanding reduced size. Based on these considerations, when there is a choice between multiple series-parallel connection and multiple parallel-series connection, multiple parallel-series connection (series-connected groups of multiple batteries connected in parallel) is often selected.
A bus-bar, which is described below, has been previously developed as a connecting piece to electrically connect battery electrodes together. A rectangular battery has circular cylindrical positive and negative electrode terminals protruding from both ends of its top surface. A bus-bar straddles adjacent rectangular batteries to connect positive and negative electrode terminals (refer to Japanese Laid-Open Patent Publication 2008-91183).
The bus-bar has a shape such as rectangular or elliptical with two identically sized circular holes, and electrode terminals insert through those holes. The electrode terminals that protrude from a rectangular battery are threaded to accept nut attachment. As shown in FIG. 1 of JP 2008-91183, nuts are threaded onto the electrode terminals on top of a bus-bar and tightened to attach the bus-bar to the electrode terminals. A plurality of rectangular batteries is electrically connected in series by the bus-bars.
To connect batteries in a multiple parallel-series configuration consistent with techniques described for series-connection in JP 2008-91183, the following method can be devised. For example, to connect twenty batteries in four series-connected groups of five batteries connected in parallel (five parallel-four series), first groups of five batteries are stacked together with like-polarity electrode terminals lined-up on each side to form four blocks of batteries. Next, the five positive electrode terminals of each block are connected together with a bus-bar provided with five holes. Similarly, the five negative electrode terminals of each block are connected together with a bus-bar provided with five holes to connect the batteries in each block in parallel. At the positions where these four blocks are joined in series, new connecting hardware must be added unfortunately increasing the number of component parts. If the number of component parts is increased, the system has the drawback that assembly becomes more complex, contact resistance problems can develop, and battery output can degrade as a result.
The present invention was developed to resolve the problems described above. Thus, it is an object of the present invention to provide a power source apparatus that can connect battery electrode terminals together in a simple manner for multiple parallel-series connection (series-connected groups of multiple batteries connected in parallel) and improve battery output as well.